Inventory Placement is an optional service that allows all quantities of a single MSKU to go to the same warehouse. This does not prevent split shipments.  If you have 10 of an item and 12 of another item, you can still have the quantities of the two items split to different fulfillment centers with Inventory Placement turned ON.

(See the attachment or go here for more details.)

Send single Merchant SKUs to a single fulfillment center:

This option enables you to send all Units of a single Merchant SKUs to a single fulfillment center determined by Amazon during the shipment creation process at a per-unit cost. In addition, most Standard-Size products will be combined into the same shipment. Certain products, including those in the following categories, may be shipped to different fulfillment centers even if you have enabled the Inventory Placement Service:

Apparel/Jewelry/Shoes/Media/Oversize Products with special prep or handling requirements.

Furthermore, Merchant SKUs that are enabled for stickerless, commingled inventory may be shipped to a different fulfillment center or placed in a separate shipment than Merchant SKUs that are not eligible for stickerless, commingled inventory.

*** Please be mindful when using IPS or if you choose to use it some times and then DISABLE it.  IPS being ENABLED when not needed can cause unnecessary fees to be deducted from your sales. For REPORT users, IPS fees will be displayed under Other Selling Fees. ***